1. Field of the Invention
The present invention relates to an automotive side sill reinforcement structure which is preferable to increase the bending stiffness and torsional stiffness of a side sill with a simple construction.
2. Description of the Related Art
side sills disposed on left and right sides of a vehicle to extend in a longitudinal direction are members constituting side bodies of the vehicle. Front pillars and center pillars are provided to rise from the respective side sills, so that a roof panel is mounted on the respective pillars, whereby a framework for a passenger compartment is formed. Thus, the side sills constitute a member which forms a base for the passenger compartment framework and determines the stiffness of the vehicle body.
For example, the deformation of the passenger compartment framework of a vehicle that occurs when another vehicle collides against the side thereof needs to be restrained to a minimum level, and the reinforcement of the side sill plays a crucial role.
Deformed conditions of side sills resulting from side collisions of vehicles will be described below.
FIGS. 5A, 5B are explanatory views of a conventional side sill.
FIG. 5A is a perspective view showing the vehicle body framework construction of a vehicle, in which a front pillar 101 is made to rise from a front end of a side sill 100, a center pillar 102 is made to rise from a middle portion of the side sill, a roof side rail 103 is attached to upper ends of the front pillar 101 and the center pillar 102, a roof rail 104 is made to extend between the left and right roof side rails 103, and front floor cross members 105 are made to extend between the left and right side sills 100, so that a passenger compartment framework is formed.
FIG. 5B is a sectional view taken along the line V—V in FIG. 5A, and as is seen therefrom, the side sill 100 includes an outer member 108 and an inner member 111 which is attached to a passenger compartment side of the outer member 108.
The deformation of the side sill 100 will be described below which would result when a load P corresponding to a load that would be applied during a side collision of vehicles is applied to the center pillar 102 above the side sill 100 in a direction indicated by an arrow.
FIG. 6 is a perspective view for describing the deformation of a conventional side sill and is an approximation model for the side sill and the center pillar shown in FIGS. 5A, 5B.
Namely, end portions of the side sill 100 are supported by support members 112, 113 which function as a fulcrum, and an upper end portion of the center pillar 102 is supported by a support member 114 which functions as a fulcrum.
Then, the load P is applied to the center pillar 102 above the side sill 100 in the direction indicated by the arrow.
FIGS. 7A, 7B are first explanatory views explaining how the applied load P deforms the conventional side sill, in which FIG. 7A is a view as viewed in a direction indicated by an arrow VII in FIG. 6, and FIG. 7B is a view as viewed in a direction indicated by an arrow VII′ in FIG. 6.
In FIG. 7A, assuming that a load applied point on the center pillar 102 is A, a cross-sectional center of the side sill 100 is B, and a distance between the load applied point A and the cross-sectional center B is L, a torsional moment PL is generated in the side sill 100.
In addition, in FIG. 7B, a bending moment PM is generated in the side sill 100 between the support members 112, 113 at the same time as the torsional moment PL is generated.
FIGS. 8A, 8B are second explanatory views explaining the deformation of the conventional side sill by the load P, in which enlarged views of main parts of the side sill 100 and the center pillar 102 are used for the explanation.
In FIG. 8A, a shear force is generated in the side sill 100 in which the torsional moment PL is generated, and assuming that the side sill 100 is constituted by an upper wall 100a, a lower wall 100b, a left wall 100c and a right wall 100d, for example, a tensile force TE inclined relative to the axis of the side sill 100 and a compressive force CM normal to the tensile force TE are generated in the upper wall 100a and the right wall 10d, respectively.
In FIG. 8B, in the side sill 100 in which the bending moment PM is generated, in the direction of a J—J line (which extends horizontally to intersect the axis of the side sill 100 at right angles), a tensile force (which is represented by “Tens” and “−”, and which tends to increase as it moves away from the cross-sectional center B along the J—J line) is generated, as a whole, on a left wall 100c side of the cross-sectional center B, and a compressive force (which is represented by “Comp” and “+” and which tends to increase as it moves away from the cross-sectional center B along the J—J line) is generated, as a whole, on a right wall 100d side thereof.
FIGS. 9A, 9B are third explanatory views explaining the deformation of the conventional side sill by the applied load, in which FIG. 9A is a perspective view showing tensile force and compressive force which are generated in the side sill 100, and FIG. 9B is a cross-sectional view showing the same forces.
In FIG. 9A, a compressive force CC is generated in the upper wall 100a and the right wall 100d, and a tensile force TT is generated in the left wall 100c and the bottom wall 100b. 
The compressive force CC and the tensile force TT are each a resultant force of the compressive force CM and the tensile force TE shown in FIG. 8A, and the compressive force CC increases as it approaches a corner portion 100e where the upper wall 100a intersects with the right wall 100d, whereas the tensile force TT increases as it approaches a corner portion where the left wall 100c intersects with the lower wall 100b. 
Namely, in FIG. 9B, the compressive force (which is represented by “Comp” and “+”) is generated in the cross section of the side sill 100 on one side of a K—K line as a boundary, whereas the tensile force (which is represented by “Tens” and “−”) is generated on the other side thereof.
As a result, in the side sill 100 where the aforesaid two kinds of moments, that is, the torsional moment PL (refer to FIG. 7A) and the bending moment PM (refer to FIG. 7B) are generated, a bending moment around the K—K line or a bending moment FF which attempts to bend the side sill 100 in a direction in which an N—N line which intersects with the K—K line at right angles extends is generated by a combination of the torsional moment PL and the bending moment PM.
Thus, the compressive force is applied on an AA side of the cross section (the one side of the K—K line as a boundary) of the side sill 100, and the tensile force is applied on a BB side of the cross section (the other side of the K—K line) of the side sill 100. Consequently, in order to increase the stiffness of the side sill 100, the stiffness in the N—N line needs to be enhanced.
FIGS. 10A, 10B are fourth explanatory views explaining the deformation of the conventional side sill by the applied load, in which FIG. 10A is a cross section of the actual side sill 100 and FIG. 10B is a cross section showing a condition where the bending moment FF explained in FIGS. 9A, 9B is applied to the side sill 100.
On the actual side sill 100 shown in FIG. 10A, a stepped portion 116 is provided at an upper portion 115 of the outer member 108 for preventing the penetration of rain water into the passenger compartment, and as shown in FIG. 10B, the upper portion 115 of the outer member 108 is forced to deform largely in the vicinity of the stepped portion 116 from an initial condition indicated by phantom lines to a condition indicated by solid lines when the bending moment FF acts on the upper portion of the outer member 108 as the compressive force.
Consequently, in the event that the side sill 100 is reinforced in the direction in which the N—N line extends, the bending stiffness of the side sill 100 can be enhanced.
FIG. 11 is a graph showing the stiffness of the conventional side sill, and the axis of ordinate represents the horizontal load P that is applied to the center pillar as shown in FIG. 5B, whereas the axis of abscissa represents the displacement δ of the side sill in the horizontal direction by the load P.
In the figure, reference numeral 120 denotes a side sill including the outer member 108, the inner member 111 and a reinforcement member 121 which is interposed between the outer member 108 and the inner member 111. The side sill 120 draws almost a similar load-displacement curve to that of the side sill 100 shown in FIGS. 5A, 5B. Namely, in the event that a load is inputted sideways to the center pillar, the provision of the reinforcement member 121 shaped as shown in the figure can provide little advantage.
This is because the reinforcement member 121 does not provide a construction which can restrain the deformation of the outer member 108 of the side sill 120 since the reinforcement member is provided longitudinally whereas the bending moment FF resulting in the side sill 100 is generated in a diagonal direction, whereby a load of large magnitude is applied, in particular, to the upper portion 115 of the outer member 108 to thereby deform the outer member 108 of the side sill 100.
In addition, known as a side sill reinforcement structure is an “automotive side sill structure” disclosed in JP-A-2000-238666.
As shown in FIG. 12, the same Japanese Unexamined Patent Publication is a side sill structure in Which a side sill 203 includes a side sill outer 204 provided on an outer side of a vehicle body, a side sill inner 206 provided on an inner side of the side sill outer 204, a side sill strength 213 provided between the side sill outer 204 and the side sill inner 6 and adapted to connect the side sill outer 204 and the side sill inner at upper and lower portions thereof and a reinforcement plate 230 attached so as to close the back of a protruding portion 218 provided on the side sill strength 213.
The side sill 203 is constructed such that the side sill outer 204 and the side sill inner 206 are reinforced by the side sill strength 213 and the reinforcement plate 230, and this construction increases the number of components and complicates the construction of the side sill 203.
Furthermore, the side sill strength 213 is adapted merely to connect the upper and lower portions of the side sill and is not expected, as with the reinforcement member 121 shown in FIG. 11, to contribute to the restraining of the deformation of the upper portion of the side sill outer 204.